Mars rover Curiosity's top 5 scientific discoveries

NASA's Mars rover Curiosity has already achieved its initial mission, proving that the Red Planet could have once sustained life, but one scientist says its greatest accomplishments could be in the year ahead.

"It is all part of the evolution of our understanding of Mars," Lisa May, NASA's lead program executive for Mars, told Computerworld. "We are going chapter by chapter of your favorite mystery novel, making progress to understand, what was it like, was anything there and where did the water go? With Curiosity ... we're peeling away the layers of a very complex story of a planet that could have been a sibling, if not a twin to Earth, at some point."

NASA's super rover, Curiosity, hits its second anniversary working on the Red Planet and has a series of scientific accomplishments under its belt. (Image: NASA)

For two years, the robotic rover has worked on Mars, searching for signs that the planet ever held life, even in microbial form. It also signifies that Curiosity had made it through its initial mission, which lasted the length of one Martian year, or about 687 days.

That doesn't mean that scientists are finished with Curiosity. May said NASA will work with the rover as long as it's still functioning.

"Curiosity has already met its mission success criteria, but there's always the intention of continuing as long as our spacecraft lets us," May said. "We have spent $2.5 billion to send this spacecraft to Mars, and we'll use it to learn and explore as long as we can."

After a journey of more than eight months and traveling a distance of 350 million miles, Curiosity used a supersonic parachute, a tether and rockets to safely alight on Mars. NASA scientists called the time from when the spacecraft entered the Martian atmosphere to when it touched down on the planet's surface, " seven minutes of terror" because a 14-minute communication delay between a signal from Mars reaching the Earth meant they had no idea what was happening during that time.

Once it was safely on the ground, scientists and engineers quickly set Curiosity to work, and in the past two years, the rover has made significant progress working on Mars.

Here are the top five scientific discoveries Curiosity has made so far:

1.Ancient Mars could have held life: Thanks to Curiosity, scientists found that ancient Mars likely had the right chemistry to support living microbes, according to NASA. By drilling into Martian rocks, the rover discovered what are believed to be the key ingredients for life -- carbon, hydrogen, oxygen, phosphorus and sulfur.

Analyzing the makeup of the rocks, the rover found clay minerals and not too much salt. That tells researchers there once might have been drinkable water on the Red Planet.

"We have found the minerals that we are familiar with as the building blocks of life," May said. "We've also found places that had water, which was a source of energy. There were places where the water was neither too acidic nor too salty. There are areas where the environment would have been habitable billions of years ago. That's probably the biggest things we found."

2.Evidence of ancient water flows: Curiosity found rocks believed to have been smoothed and rounded by ancient water flows. The layers of exposed bedrock tell scientists a story of what was once a steady stream of water flowing about knee deep.

"It is surprising how much water persists under the surface of Mars and how much water must have been there," May said. "What happened? It either went into the rocks or out through the atmosphere."

3. Curiosity detects dangerous levels of radiation: Curiosity detected radiation levels that exceed NASA's career limit for astronauts. With this data in hand, the space agency's engineers can build spacecraft and spacesuits that are able to protect humans on deep space missions.

4. No methane, no life? In September 2013, NASA noted that the rover had not found a single trace of methane in the Martian atmosphere, decreasing the odds that there is life on Mars. Since living organisms, as we know them, produce methane, scientists had been trying to find the substance on the Red Planet, as proof that life might have once existed there. The hunt for methane continues.

5. Significant geological diversity: Scientists were surprised by the variety of soil and rock that they found in the Gale Crater, where Curiosity landed. According to NASA, Curiosity found different types of gravel, streambed deposits, what could possibly be volcanic rock, water-transported sand dunes, mudstones, and cracks filled with mineral veins. All of these yield clues to Mars' past.

NASA scientists have wanted Curiosity to study Mount Sharp and its geological layers since the robot landed on Mars Now, the rover is about two miles away and nearing an outcrop of a base layer of the mountain.

"Oh, I think this coming year is going to be even more exciting," said May. "Because we're going to get more detailed stories and compare stratigraphic layers, we're really going to learn about the history of Mars."

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